The mufflers employed in the exhausts of automotive engines are subject to great mechanical and thermal stresses which lead to their early deterioration. At the high temperatures involved, conventional rustproofing measures such as painting, galvanizing or alloying are largely ineffective against the corrosive action of sulphur oxides in the exhaust gases from within the system and of mud or slush from without. External coatings of enamel, for example, are relatively brittle and are therefore easily damaged by flying pebbles or gravel.
Aluminum and some of its alloys are highly resistant to corrosion but, because of their low melting point, cannot withstand prolonged exposure to high temperatures. Thus, it has already been proposed to make mufflers by high-pressure aluminum casting; such mufflers, however, were found suitable only for motorcycles and similar low-power vehicles.